The present invention relates to fuel pressure vessel mounting systems and more particularly to roof mounted systems for supporting a plurality of fuel pressure vessels.
The advent of low floor transit vehicles, such as buses, fueled by alternative fuels such as compressed natural gas (CNG), liquefied natural gas (LNG) or hydrogen, has resulted in the need to mount fuel storage in the form of pressurized vessels to the vehicle and preferably on the roof.
Typically, in order to achieve a driving range similar to diesel and to achieve safety standards associated with alternative fuels, a plurality of pressure vessels must be used. In order to reduce the weight of such fuel storage systems, lightweight composite pressure vessels and mounting systems are used.
In order to meet ANSI/AGA NGV2 and CSA B51 certification in both the U.S. and Canada, the mounting systems must be designed to accommodate radial and axial growth of the fuel pressure vessels as a result of pressurization of the pressure vessel and further, must withstand dynamic loading as a result of normal operation and in the event of a crash. The dynamic loads which must be safely restrained in the event of a crash are specified in terms of multiples of gravity. The loading design is dependent on the orientation of the vessel. In Canada, where pressure vessels are typically oriented in the same direction as travel of the vehicle, the design dynamic loading must be at least 20 g in the longitudinal direction of the vehicle and 8 g in any other direction. These loads supersede those required for normal operation and are generally more stringent than those imposed in the U.S., where vessels are oriented in the same direction. Further, a maximum allowable deflection of 0.5 inches (12.5 mm) for mounting brackets is required when tested at 8 g. When pressure vessels are mounted crosswise to the direction of travel, such as is the convention in Europe and Japan, the current design crash loads are 100 g in all directions. The standards periodically change.
In 1998, Lincoln Composites (Lincoln, Nebr., U.S.A.), a division of Advanced Technical Products, Inc., disclosed a modular concept for roof mounting utilizing a lightweight truss frame, expandable to accommodate various lengths of pressure vessels. Integration of the modules to the bus roof is accomplished by utilizing mounting brackets that can be relocated along the length of the modules to correspond with the roof xe2x80x9chard pointsxe2x80x9d. The modular frame comprises end frames spacing two rails and a plurality of truss-like central frame members running lengthwise in the same direction as the pressure vessels and separating the pressure vessels, thus adding structural rigidity to the frame.
Other frames have been designed to meet safety requirements and weight restrictions. One such known design is that used typically for roof-mounting in low floor buses comprising a frame structure of end members and cross members. The frame has steel straps at two places along each pressure vessel, clamping each pressure vessel into the frame.
In the Lincoln Composites system described above, pressure vessels are positioned with their longitudinal axis oriented in the same direction as the longitudinal axis of the vehicle. In other known frames, fuel cells are oriented with their longitudinal axis at 90 degrees to the frame rails and to the longitudinal axis of the vehicle. The differences in orientation of the pressure vessels are representative of differences in mounting conventions between North America and those in Japan and Europe.
The known mounting systems utilize multiple-component, complete and heavy frames into which pressure vessels are mounted.
Ideally, a roof-top mounting system must be lightweight, able to meet or exceed current safety standards, comprise a minimum of structural elements, allow easy access to one or more fuel pressure vessels or cells and allow mounting of pressure vessels of various sizes.
The present invention obviates the prior art requirement for heavy frames through a combination of a unique lightweight fiber-reinforced (FRP) bracket and incorporation of the fuel vessel as part of the overall structure for supporting the vessel. The brackets are capable of accepting dynamic inertial loads imposed by the vessels under acceleration. Acceleration, unless the context suggests otherwise, includes positive and negative acceleration; negative acceleration also being known as deceleration. While discussed herein in the context of a vehicle upon which the pressure vessels are mounted, the term vehicle is understood to relate to any structure capable of movement. The composite brackets are a lightweight and strong solution to providing a balance between being stiff enough to resist inertial loading yet flexible enough to permit longitudinal expansion of the pressure vessels. Expansion occurs through filling (pressurizing) and emptying cycles and through thermal expansion and contraction.
In one broad aspect of the invention, a system is provided for securing one or more parallel pressure vessels to a structure such as a vehicle. The system comprises one or more pressure vessels each having two opposing neck ends and having a longitudinal axis; a pair of fiber-reinforced composite mounting brackets to which the pressure vessels are mounted, each bracket being a unitary member having a base adapted for mounting to the structure, each bracket being positioned at each neck end of the one or more pressure vessels and having an axis which extends substantially perpendicularly to the longitudinal axis of the pressure vessels; and neck-mounting means for mounting each pressure vessel""s neck end to each bracket, the one or more pressure vessels extending between the brackets so as to space the brackets apart and add structural rigidity to the system.
The broad system is effectively implemented using a novel bracket comprising a fiber-reinforced composite and unitary beam, the beam having an axis which is adapted to extend perpendicular to the axis of the pressure vessel, and further comprising, a base adapted for mounting to the structure; a web extending from the base, the web receiving an attachment for mounting the neck end of each of the one or more pressure vessel so as to transfer load from the neck end of the pressure vessel into the web. Preferably the web is notched for accepting the attachment, the attachment comprising a body having a laterally extending profile for fitting correspondingly into the notch and a bore adapted for mounting to the neck end of the pressure vessel; the body being secured to the web.
The bracket and system enables implementation of a novel method for mounting one or more pressure vessels to a structure, most advantageously to a structure such as a vehicle which is subject to acceleration or inertia, the method comprising the steps of: providing first and second fiber-reinforced composite brackets, each bracket having a base from which a web extends and one or more attachments formed in the web; mounting a pressure vessel at a first neck end to an attachment of the first bracket and at a second end to an attachment of the second bracket so as to mount the pressure vessels to the brackets and to space the brackets apart so as to create a structurally rigid system; and mounting the spaced first and second brackets to the structure. The brackets are capable of accepting inertial loading from the pressure vessels while flexing under the pressure vessel differential expansion such as that experienced during fill and empty cycles.